Investigators are optimistic that they can soon locate wreckage from the missing Malaysian Air jet in the Indian Ocean after reacquiring acoustic pings that may emanate from the flight recorders.

Australian search vessel Ocean Shield detected a signal two more times, a possible step toward narrowing the hunt enough to deploy a robot submarine that can scan the sea floor. The sounds are consistent with those emitted by beacons on Flight 370’s black boxes, said retired Air Chief Marshal Angus Houston, who heads Australia’s Joint Agency Coordination Centre.

“Hopefully with lots of transmissions, we will have a tight, small area — and hopefully in a matter of days we will be able to find something on the bottom,” Houston told reporters today in Perth.

Hearing the pulses again after a pair of contacts over the weekend solidified authorities’ growing confidence that they are zeroing in on the debris a month after Flight 370 vanished. Determining the right zone for underwater surveillance is pivotal before committing the Ocean Shield’s sonar-equipped submersible.

Fading power reserves for the beacons on the Boeing Co. 777-200ER’s cockpit-voice and flight-data recorders are adding urgency to the search. The batteries are nearing the end of their lifespan after the Malaysian Airline System Bhd. plane vanished en route to Beijing from Kuala Lumpur on March 8. On board were 239 passengers and crew members.

Malaysia Optimism

Malaysia is “cautiously more optimistic,” Acting Transport Minister Hishammuddin Hussein said in a Twitter posting after Houston’s press conference. “Pray latest leads will help us all move ahead.”

The Ocean Shield is pulling a U.S. Navy towed pinger locator through the water to listen for signals from the black-box beacons. The unmanned sub, the Bluefin-21, is ready to launch once the search zone is refined, Houston said. Water depths in the area exceed about 4,500 meters (14,800 feet).

It’s good news that the Ocean Shield is detecting signals as the beacons’ strength wanes, Fish said. Sound from the plane’s pingers travels shorter distances when the signal weakens.

‘Getting Closer’

“If they are dying and they’re picking them up still, they’re getting closer,” said Fish, whose company has helped recover numerous aircraft and their black-box recorders from underwater.

The pingers have a range of about 2 miles (3.2 kilometers), according to the manufacturer, Dukane Seacom, a unit of Hollywood, Florida-based Heico Corp. The black-box maker is Morris Township, New Jersey-based Honeywell International Inc.

Dukane Seacom has analyzed data collected on the pings and concluded that the signals “would be very difficult to be anything else than the acoustic signature of a beacon,” President Anish Patel said in a telephone interview. “Does it have to be the black box beacon? It could be something else, but the likelihood of it being something else is doubtful.”

Analysis of pings heard by the Ocean Shield during the weekend determined that a “very stable” signal was detected at 33.331 kilohertz and it consistently pulsed at 1.106-second intervals, JACC’s Houston said. Two signals — one lasting two hours and 20 minutes and the other for 13 minutes — were detected after the deployment of the pinger locator, which is being operated by a crew from Phoenix International Holdings Inc. of Largo, Maryland.

Design Frequency

Dukane Seacom’s pingers are supposed to pulse at 37.5 kilohertz. While the units are designed to have a tolerance of plus or minus one kilohertz from the intended frequency, the difference may not be significant, Patel said.

A beacon recovered from Air France Flight 447, the jet that crashed in the South Atlantic in 2009, and then tested was found to have shifted frequency, transmitting at 34 kilohertz, Patel said.

According to a map from the Australian Maritime Safety Authority, the four pings heard so far came from a triangular zone with one side almost 30 kilometers long. The distances between the four detections may be explained by the fact that there are two black boxes, each with a pinger, Fish said.

Even after sending the Bluefin-21 into the water to prowl the ocean bottom with sonar, the search may face complications because of a blanket of silt several meters deep on the seabed, Houston said.

‘Very Challenging’

“I am now optimistic that we will find the aircraft, or what is left of the aircraft in the not-too-distant future,” Houston said. “But we haven’t found it yet because this is a very challenging business.”

Houston said the location of the pings is lining up with other evidence of where the plane may be. The underwater sounds were detected near where analysts estimate a final, partial satellite signal was received from the Malaysian plane, Houston said.

That last pulse to an Inmarsat Plc satellite is where investigators believe the 777’s two engines may have flamed out, Houston said. “It’s probably significant in terms of the end of powered flight,” he said.

The jet’s disappearance is now the longest in modern airline history, baffling authorities because contact was lost less than an hour into a routine trip as Flight 370 headed north over the Gulf of Thailand. After vanishing from radar, the wide-body craft doubled back, flew over Peninsular Malaysia and on into some of the world’s most remote waters.

While the motive behind that heading remains unknown, Flight 370 was deliberately steered south on a path ending in the Indian Ocean, Malaysian Prime Minister Najib Razak has said.